The present invention provides pressure-sensitive adhesives (PSAs) and protective coatings based on one or more polymers containing a moiety like benzocyclobutenone (BCBO) that is capable of generating a ketene under UV irradiation.
PSAs are a distinct category of adhesives which, in dry (solvent-free) form, are aggressively and permanently tacky at room temperature and firmly adhere to a variety of dissimilar substrates upon mere contact, without need of more than finger or hand pressure. PSAs do not require activation by waters heat, or solvents; and have sufficient cohesive strength to be handled with the fingers. The primary mode of bonding for a PSA is not chemical or mechanical but, rather, a polar attraction to the substrate, and always requires initial pressure to achieve sufficient wet-out onto the surface to provide adequate adhesion.
Both rubber-based and acrylic-based PSAs are known. In 1966, C. Dalquist identified a one-second creep compliance greater than 1xc3x9710xe2x88x926 cm2/dyne as the efficient contact criterion for a good PSA. A more recent discussion of PSAs in the Handbook of Pressure Sensitive Adhesive Technology (2d Edition) D. Satas, ed. (1989), (hereafter, xe2x80x9cHandbookxe2x80x9d), pages 172-176, incorporated by reference herein, identifies glass transition temperature (Tg) and modulus (Gxe2x80x2) at the application (use) temperature as the most important requirements for PSA performance. Both properties are a function of the identities and amounts of monomers that comprise the PSA polymer(s). Thus, poly(acrylic acid) is not a PSA, but a copolymer of acrylic acid and a high mole % of 2-ethylhexyl acrylate is.
The typical values of Gxe2x80x2 and Tg for label and tape PSAs are described in the Handbook. For a tape, Gxe2x80x2 at room temperature ≈5xc3x97105 to 2xc3x97106 dyne/cm2, and Tg≈xe2x88x9215xc2x0 C. to 10xc2x0 C.; while labels have a lower value of Gxe2x80x2 at room temperature, i.e., about 2xc3x97105 to 8xc3x97105 dyne/cm2. Tg requirements for cold temperature, permanent, and removable applications are different, as is known in the art. Thus, cold temperature label PSAs generally require a Tg of from about xe2x88x9230xc2x0 C. to xe2x88x9210xc2x0 C.
High performance PSAs are normally characterized by the ability to withstand creep or shear deformation at high loadings and/or high temperatures, while exhibiting adequate tack and peel adhesion properties. A high molecular weight provides the necessary cohesive strength and resistance to shear deformation, while a low modulus allows the polymer to conform to a substrate surface upon contact.
High molecular weight, or the physical effect of a high molecular weight, can be obtained by primary polymerization of monomers to form a backbone of long chain length, and/or by creating a high degree of inter chain hydrogen bonding, ionic association, or crosslinking between polymer chains. For solvent-based adhesives, it is preferred to crosslink after polymerization (so-called xe2x80x9cpost-polymerization crosslinking), which avoids processing difficulties such as coating a highly viscous polymer network. Post-crosslinking is also commonly used for water-based PSAs to enhance cohesive strength. Post-curing is also sometimes used with hot melt PSAs, although radiation curing is more commonly employed with such systems, to avoid thermal cure during the coating process.
Thermal crosslinking and photoinitiated crosslinking are well-known approaches to introducing crosslinks between polymer chains. In most photoinitiated (photocuring) systems, a post-added photoinitiator is employed and reacts with an acrylate, methacrylate, allyl, epoxy, or other functional group on the polymer or oligomer to be cured. Ultraviolet (UV) radiation causes curing. In such systems, a photoinitiator residue remains, and can have a deleterious effect. For example, in medical applications, such residues can cause skin irritation. In electronics applications, the residues can introduce undesirable contamination to the coated device. In addition, the curing process used in post-added photoinitiator systems is usually oxygen-sensitive. There is a need for high performance PSAs that have a good balance of tack, peel and shear strength, and that do not suffer from the drawbacks of photoinitiator residues and incomplete curing due to the presence of oxygen.
Another area where improved polymeric compositions are needed is protective coatings. These coatings include marine coatings, coatings for automotive components, scratch-resistant and dust-resistant coatings, top coats for printed or imprintable materials, and other coatings that provide a substrate with a protective barrier. For some applications, processing constraints limit the types of coatings that will work. For example, many electronic components are damaged by high temperatures and are thus unsuitable for protection with thermally cured coatings, unlike automotive finish applications. UV-curable coatings are the preferred choice for electronic components. However, electronic components are also sensitive to contaminants, particularly if the contaminants can cause a build-up in static charge or a change in the magnetic properties of the component. A need exists for improved protective coatings for electronic components.
Polymeric protective coatings having a low surface energy and chemical inertness are also desired in a variety of applications. Low surface energy materials are important for applications requiring reduced wetting and adhesion to other compounds; for instance, they can be used as coatings for suppressing marine bioadhesion, for membranes with reduced biofouling, and as protective implants. Typically, such coatings have a surface energy of 16-25 dyne/cm. Fluropolymeric coatings are representative. An inherent drawback of such low surface energy, fluropolymeric coatings is poor adhesion to some substrates, such as ABS. This can lead to premature deprotection of the surface. On the other hand, acrylic polymers or resins have been widely used as coatings for many applications due to their good adhesion properties, UV stability, and optical clarity, etc. However, the higher surface energy ( greater than 33 dyne/cm) of acrylic polymers excludes them from many of the above-mentioned applications. Although in recent years, efforts have been made in the synthesis of fluorinated acrylic coatings through copolymerization, surface grafting, and polymer blend techniques, the use of acrylic polymers with fluropolymer blocks for coatings has not received much attention. A need exists for improved acrylic-fluropolymeric hybrids useful in a variety of coating applications.
According to one aspect of the present invention, high performance PSAs having a balance of tack, peel and shear strength are provided, and comprise at least one copolymer formed of a plurality of monomers that includes at least one ketene-forming monomer, e.g., benzocyclobutenone (BCBO), with the identity and amount of the monomers being selected such that the resulting copolymer is a PSA. One such PSA is formed by curing a polymer formed from a plurality of monomers that includes at least one ketene-forming monomer and at least two acrylic monomers, or at least one each of a ketene-forming monomer, an acrylic monomer, and a non-acrylic monomer. In another embodiment, the plurality of monomers includes at least one ketene-forming and at least one hydroxy-functional monomer or another monomer capable of crosslinking with a ketene moiety in response to elevated temperature or UV or EB radiation. Another PSA is formed by curing a mixture of two or more polymers, at least one of which is formed from a plurality of monomers that includes at least one ketene-forming monomer, and at least one other polymer is formed from a second plurality of monomers. In some embodiments, the first and/or second plurality of monomers includes at least one hydroxy-functional monomer, while in other embodiments one or more other reactive monomers are included. When the mixture of polymers is heated or irradiated with UV or EB radiation, it cures to a PSA having a high cohesive strength.
Other PSAs comprising polymers formed from BCBO and other monomers are also provided.
In another aspect of the invention, polymeric compositions that function as protective coatings are provided, and comprise at least one copolymer formed of a plurality of monomers that includes at least one BCBO or other ketene-forming monomer. The compositions are UV-curable and suitable for use as protective coatings for electronic components and in a variety of other applications.
Unlike conventional UV-curable systems, the new PSAs and protective coatings contain no photoinitiator residues after curing.
According to one embodiment of the invention, a PSA is provided and comprises at least one copolymer formed of a plurality of monomers that includes at least one xe2x80x9cketene-forming monomerxe2x80x9d, i.e., a monomer capable of forming a xe2x80x9cketenexe2x80x9d (Rxe2x95x90Cxe2x95x90O) when heated above room temperature or irradiated with ultraviolet (UV) light or electron beam (EB) radiation. After being cured with heat or radiation, the copolymer has a high cohesive strength and is useful in a variety of tape, label, and other applications.
A particularly preferred class of ketene-forming monomers is referred to herein as benzocyclobutenone (BCBO) monomers. When exposed to heat or UV or EB radiation, BCBO undergoes a rearrangement and forms a ketene (Rxe2x95x90Cxe2x95x90O), which is highly reactive towards alcohols, as shown in Scheme 1:
It has now been discovered that high cohesive strength PSAs can be prepared by first copolymerizing one or more BCBO or other ketene-forming monomers with a plurality of acrylic and/or non-acrylic monomers, preferably using conventional free-radical polymerization, and then curing the copolymer with UV or EB radiation and/or heat.
As used herein, the term xe2x80x9cBCBO monomerxe2x80x9d refers to any copolymerizable monomer containing the BCBO moiety, i.e., any BCBO-containing monomer that is capable of undergoing free-radical polymerization with other free-radical polymerizable monomers. Non-limiting examples include BCBO acrylate, BCBO methacrylate, and BCBO acrylamide, the structures of which are provided below: 
More generally, BCBO monomers have a formula 
where Z is a functional group or moiety capable of copolymerizing with one or more ethylenically unsaturated monomers. For example, Z can be a vinyl group (H2Cxe2x95x90CHxe2x80x94), acrylic group (H2Cxe2x95x90CHC(O)Oxe2x80x94), methacrylic group (H2Cxe2x95x90C(CH3)C(O)Oxe2x80x94), etc. Z can be bound directly to the BCBO moiety, or spaced apart therefrom by, e.g., a group such as an alkylene (xe2x80x94CH2"Parenclosest"n.
BCBO acrylamide xe2x80x9cBCBO-AMxe2x80x9d)can be prepared according to the method disclosed in U.S. Pat. No. 5,869,693, the contents of which are incorporated herein by reference. The same patent discloses the preparation of 5-hydroxy BCBO. BCBO acrylate and BCBO methacrylate can be prepared by reacting 5-hydroxy BCBO with acryloyl chloride or methacryloyl chloride, respectively. Reaction conditions are presented infra.
The term xe2x80x9cacrylic monomerxe2x80x9d refers to any monomer in the class of free-radical polymerizable monomers that includes acrylic acid, methacrylic acid, acrylamide, methacrylamide, acrylonitrile, and derivatives thereof. Non-limiting examples include alkyl (meth)acrylates, hydroxyalkyl (meth)acrylates, alkyl (meth)acrylamides, alkyl di(meth)acrylates, ethylenically unsaturated carboxylic acids, epoxy (meth)acrylates (e.g., glycidyl (meth)acrylate), ethoxylated (meth)acrylates, cyanoacrylates, etc. Also included are acrylic-, (meth)acrylamido-, and (meth)acrylonitrile-terminated macromers.
Alkyl (meth)acrylates are well known and commonly used in the preparation of acrylic PSAs. Nonlimiting examples include methyl, ethyl, propyl, butyl, pentyl, hexyl, octyl, nonyl, decyl, undecyl, and dodecyl acrylate, and the corresponding methacrylates. Cyclic acrylates and methacrylates, e.g., cyclohexyl acrylate, isobornyl acrylate, are also included. (Meth)acrylates with 4-12 carbon atoms per alkyl group are considered xe2x80x9csoftxe2x80x9d monomers, and form copolymers with lower Tg""s than so-celled xe2x80x9chardxe2x80x9d monomers, e.g., methyl (meth)acrylate, ethyl methacrylate, etc.
Non-limiting examples of hydroxyalkyl (meth)acrylates include hydroxyethyl acrylate (HEA), hydroxyethyl methacrylate (HEMA), and hydroxypropyl acrylate.
Nonlimiting examples of alkyl (meth)acrylamides include acrylamide, methacrylamide, N-methylol (meth)acrylamide, N-ethanol acrylamide, N,N-dimethyl (meth)acrylamide, N-t-butyl acrylamide, octyl-acrylamide, etc.
Nonlimiting examples of alkyl di(meth)acrylates include dimethylaminoethyl di(meth)acrylate, 1,6-hexanediol diacrylate, diethyleneglycol di(meth)acrylate, triethyleneglycol di (meth)acrylate, etc.
Nonlimiting examples of ethylenically unsaturated carboxylic acids include acrylic acid, methacrylic acid, itaconic acid, xcex2-carboxyethyl acrylate (xcex2-CEA), and higher oligomers of acrylic acid.
(Meth)acrylic-, (meth)acrylamido-, and (meth)acrylonitrile-terminated macromers are rubber or acrylic polymers of small to medium chain length (NW from about 2,000 to 25,000) terminated with a meth)acrylic, (meth)acrylamido, or (meth)acrylonitrile functional group or example, Shell Chemical Co. (Houston, Tex.) manufactures a research product, HPVM-1251, which it calls a xe2x80x9cKraton Liquid(trademark) polymer. HPVM-1251 is a methacrylate-functional poly(ethylene/butylene) polymer, of 4000 molecular weight, having a single methacrylate group at one end of the polymer. The preparation of (meth)acryl-terminated ethylene-propylene and ethylene/butylene macromers and their use in preparing acrylic-rubber hybrid graft copolymers are described in U.S. Pat. No. 5,625,005, which is incorporated by reference herein.
The term xe2x80x9cnon-acrylic monomerxe2x80x9d refers to a free-radical polymerizable monomer having a vinyl or other ethylenically unsaturated group, other than acrylic monomers. Non-limiting examples include allylic monomers, styrenic monomers (e.g., styrene, xcex1-methyl styrene, t-butyl-styrene, 4-methoxy-styrene, 3-ethyl-styrene, 4-ethyl-styrene, and 1,4- or 1,3 divinyl-benzene), N-vinyl lactams (e.g., N-vinyl pyrrolidone), vinyl pyridine, vinyl esters (e.g., vinyl acetate, vinyl butyrate, vinyl propionate, vinyl isobutyrate, vinyl valerate, and vinyl versitate), sodium vinyl sulfonate, and dialkyl maleates and fumarates (e.g., dioctyl maleate, di-ethylhexyl fumarate, etc.).
An extended list of acrylic and non-acrylic monomers used to prepare PSAs is found in Appendix 15A of the Handbook, at pages 444-450, incorporated by reference herein and attached hereto as Appendix I.
A PSA formed of a plurality of monomers, including at least one BCBO or other ketene-forming monomer, is prepared using solvent, emulsion, hot-melt, or other free-radical polymerization, using techniques and reagents well known in the art. Nonlimiting examples are found in the following patents: U.S. Pat. No. 5,164,444, U.S. Pat. No. 5,563,205, and WO 97/11996, each of which is incorporated herein by reference. Acrylic xe2x80x9cwarm meltxe2x80x9d polymerization described below) can also be used.
In one aspect of the invention, high performance PSAs are prepared by curing a copolymer of at least one copolymerizing BCBO monomer and a plurality of acrylic and/or non-acrylic monomers. The identity and amount of the monomers are selected such that the copolymer is functional as a PSA and cures to a high cohesive strength. One embodiment of this aspect of the invention is a PSA formed from at least one BCBO monomer and at least two acrylic monomers, for example, at least one alkyl acrylate and a hydroxyalkyl acrylate. Another embodiment is a PSA formed from at least one BCBO monomer, at least one acrylic monomer, and at least one non-acrylic monomer. In another embodiment, a PSA is formed from at least one BCBO monomer, at least one xe2x80x9csoftxe2x80x9d monomer, and at least one hydroxy-functional monomer and/or at least one ethylenically unsaturated carboxylic acid. The plurality of monomers can additionally include at least one xe2x80x9chardxe2x80x9d monomer. As used herein, the term xe2x80x9csoft monomerxe2x80x9d refers to a monomer which, when homopolymerized, forms a polymer having a Tg less than 0xc2x0 C., more preferably, Tg less than xe2x88x9225xc2x0 C. Nonlimiting examples include alkyl acrylates having 4 to 12 carbon atoms in the alkyl group thereof. The term xe2x80x9chard monomerxe2x80x9d refers to a monomer which, when homopolymerized, forms a polymer having a Tg greater than 0xc2x0 C. Nonlimiting examples include vinyl esters, styrene, xcex1-methyl styrene, methyl acrylate, methyl methacrylate, ethyl methacrylate, and amide monomers.
In any of these embodiments, a small amount of chain transfer agent can be included in the monomer mixture to control molecular weight of the copolymer. A nonlimiting example of a chain transfer agent is n-dodecyl mercaptan (n-DDM).
A more specific, non-limiting example of a PSA according to the present invention is prepared from the monomers 2-ethylhexyl acrylate (2-EHA), butyl acrylate (BA), methyl methacrylate (MMA), methacrylic acid (MAA), acrylic acid (AA), 2-hydroxyethyl acrylate (2-HEA), and BCBO acrylamide (BCBO-AM), with a small amount of DDM added as a chain transfer agent. Numerous other permutations, with fewer or more monomers, can be prepared and are included within the scope of the invention. All that is required for this aspect of the invention is that the plurality of monomers include at least one BCBO or other ketene-forming monomer and a combination of other monomers that yield a copolymer having PSA behavior (described above).
Forming a copolymer that includes both a BCBO monomer and a hydroxy-functional monomer (for example, 2-HEA, HEMA, etc.) ensures that the polymer will be susceptible to UV-crosslinking through reaction of a photolytically rearranged BCBO moiety (i.e., a ketene) and a hydroxyl group, according to Scheme 1 above. However, it has beer discovered that even copolymers made from a plurality of monomers that does not include hydroxy-functional monomers also can be UV-cured to a high cohesive strength, particularly if another reactive group, such as a carboxylic acid, is present.
In another aspect of the invention, two or more distinct polymers are prepared and then crosslinked. At least one of the polymers is formed from a plurality of monomers that includes at least one BCBO or other ketene-forming monomer. A second polymer s formed from a second plurality of monomers. In some embodiments, the second plurality of monomers includes one or more hydroxy-functional monomers. In another embodiment, the second plurality of monomers includes some other functional group capable of reacting with a ketene during crosslinking. When heated or exposed to UV radiation, the two or more polymers cure to a high cohesive strength PSA or protective coating. A nonlimiting examples of this embodiment is shown in Scheme 2, with covalent crosslinks denoted by xe2x80x9cX.xe2x80x9d
A variation on this aspect of the invention uses one or more polyhydric alcoholsxe2x80x94for example, polyethylene glycol (PEG)xe2x80x94which can crosslink with one or more BCBO moieties (or other ketene-forming monomers) when cured with heat or UV light. The approach is similar to that depicted above in Scheme 2, except that PEG molecules (or other polyhydric alcohols) are the source of hydroxyl groups.
The amount of BCBO monomer employed in a given formulation depends on the degree of crosslinking that is desired, but, in general, is rather small, e.g., less than about 1% by weight (more preferably, about 0.2 to 0.5%) in the case of a PSA, and up to about 10% being used in the case of a film or protective coating. (Weight percentages are expressed based on the total weight of al monomers.) Non-BCBO monomers make up the bulk of the copolymer. In general, the more BCBO monomer(s) present in the polymer(s), the greater the degree of crosslinking that will result, with the crosslinked polymeric composition exhibiting greater cohesive strength (and resistance to shear), but also less tackiness than a less-highly crosslinked material. The identity and amount of non-BCBO monomers included in a given formulator are tailored to yield a PSA having any desired set of properties. Nonlimiting examples of such properties include shear strength, tackiness, polarity, usefulness at a particular temperature and/or humidity, adhesion to particular substrates, etc. Thus, in some embodiments, it may be preferred to include a major amount of alkyl acrylates, with a minor amount of polar monomers, hard monomers, etc. In other embodiments, one or more particular monomers may be preferred.
After ore or more copolymers are prepared, a PSA construction can be made, using fabrication techniques well known in the art. The copolymer or mixture of copolymers is coated on or otherwise applied to a substrate, as a hot melt, a solution, or an emulsion. Prior to application to a substrate, the copolymer(s) can be, and preferably are, compounded with one or more fillers, pigments, thickeners, antioxidants, defoamers, tackifiers, or other additives well known in the art.
A particularly convenient mode of application is direct coating, where the copolymer(s) are directly applied to a moving web (substrate) as a thin film. When the copolymer(s) are a solution or emulsion PSA, the major portion of volatiles is removed before the coated adhesive is cured, either by air-drying or by placing it in a forced-air oven for a few minutes. The last traces of volatiles can be removed in a forced-air oven after cure.
Nonlimiting examples of conventional PSA coating methods include slot die, air knife, brush, curtain, extrusion, blade, floating knife, gravure, kiss roll, knife-over-blanket, knife-over-roll, offset gravure, reverse roll, reverse smoothing roll, rod, and squeeze roll coating. The adhesive composition can be coated on a release liner (e.g., a silicone-coated paper or film), air-or oven-dried, and then laminated to a flexible backing, i.e., a facestock. Alternatively, the adhesive can be coated directly on a facestock, dried, and then protected with a release liner. Self-wound tapes also can be prepared, e.g., by coating he adhesive on ore side of a rape facestock. (The other side of the facestock is silicone-coated or otherwise treated so the tape can be wound up on itself without blocking.)
The adhesive coating is applied at a desirable coat weight (conveniently measured after drying) that generally lies within the range of about 15 to 100 grams per square meter (g/m2 or xe2x80x9cgsmxe2x80x9d). The coated adhesive can then be cured, either by heating it, or more preferably, by irradiating it with UV light or EB radiation.
UV curing may be carried out in a manner well known to those skilled in the art, using commercially available lamps, such as mercury lamps, fusion system lamps, and the like. A variety of bulbs, including D, Q, V, and H bulbs, are available, with spectral outputs covering a range of ultraviolet wavelengths. For example, a xe2x80x9cDxe2x80x9d bulb emits UV radiation within a spectral region of from 200 nm to 450 nm, with a relatively stronger emission in the region of 350 to 450 nm.
Coating an adhesive on a web is easier with low viscosity adhesives than it is with high viscosity adhesives. The intrinsic viscosity of polymeric materials is molecular weight-dependent, and the flow properties of low molecular weight PSA polymers are much better than those of high molecular weight PSA polymers. Unfortunately, low molecular weight PSA polymers generally have low cohesive strength, which is undesirable. Hence, the desirable features of good coatability or xe2x80x9cflow,xe2x80x9d and high cohesive strength, are at odds with one another.
With solution or emulsion PSAs, the competing features of good flow and good shear resistance (high cohesive strength) are easily accommodated because the viscosity of an adhesive solution or an emulsion is much lower than that of the actual polymers themselves. With hot melt adhesives, however, where a 100% solids adhesive is heated to a relatively high temperature (e.g., about 90xc2x0 C.) to achieve the desired flow characteristics, and no (or very little) solvent is employed, the situation is problematic. In one embodiment of the present invention, this problem is addressed by UV-curing an acrylic xe2x80x9cwarm meltxe2x80x9d copolymer. A 100% solids PSA copolymer, having a low molecular weight (e.g., Mn less than about 10,000) is heated slightly above room temperature (e.g., to about 30-40xc2x0 C.) and applied to a substrate. Because the polymer molecular weight is so low, far less heat is required to melt the polymer and obtain good flow. The desired high cohesive strength is then obtained by curing the coated PSA copolymer with UV irradiation. UV-curing is facilitated by the presence of BCBO moieties (or other ketene-forming monomers) provided in the polymer itself. This approach allows low-energy coating processes to be used to form a cured PSA construction having a desired high cohesive strength, without the use of solvent or emulsion adhesives.
In another aspect of the invention, ketene-forming compounds (e.g., BCBO compounds) are used to form polymeric compositions that can be UV-cured to form protective coatings useful in a wide variety of applications. In one embodiment, a hydroxyl-functional perfluoropolyether (PFPE) is made to react with a BCBO derivative and forms a BCBO-functional perfluoropolyether macromer (BCBO-PFPE). The BCBO-functional macromer can then be grafted onto an acrylic polymer backbone, using heat, or more preferably, UV irradiation. The resulting graft polymer is then used to form clear films or coatings that have protective as well as self-cleaning properties.
Perfluoropolyethers are soluble in common organic solvents, curable at high temperatures, as well as room temperatures, and have increased compatibility with many materials. Their low molecular weight and relatively good chemical compatibility make them ideal for use in paints or coatings where it is desirable to reduce the amount of volatile organic compounds. They also have excellent durability and outstanding stability.
Two non-limiting examples of PFPE compounds are shown below. The first (Ia) is hydroxyl-terminated at both ends of the polymer, while the second (Ib) is hydroxyl-terminated at one end only.
HOxe2x80x94CH2xe2x80x94CF2xe2x80x94Oxe2x80x94(CF2xe2x80x94CF2xe2x80x94O)pxe2x80x94(CF2xe2x80x94O)qxe2x80x94CF2xe2x80x94CH2xe2x80x94OHxe2x80x83xe2x80x83Ia
HOxe2x80x94CH2xe2x80x94CF2xe2x80x94Oxe2x80x94(CF2xe2x80x94CF2xe2x80x94O)pxe2x80x94(CF2xe2x80x94O)qxe2x80x94CF2xe2x80x94CH2xe2x80x94ORxe2x80x83xe2x80x83Ib
(R is xe2x80x94CH3 or xe2x80x94C2H5)
Both compounds are liquids at 20xc2x0 C. The diols (compounds having the formula Ia) are commercially available from Ausimont USA, Inc. (Orange, Tex.), under the trademark Fomblin ZDOL. These are oligomeric products consisting of a random distribution of xe2x80x94CF2CF2Oxe2x80x94 (C2 unit) and xe2x80x94CF2xe2x80x94 (C1 unit). They are characterized by Mw/Mn=1.2 to 2.0, p/q=0.8 to 1.2, and Mn=1000 to 4000. The diols are sold under the mark xe2x80x9cFomblin ZDOL.xe2x80x9d Monohydroxy-functional PFPEs (compounds having the formula Ib) should have similar repeat unit and molecular weight values and ratios (Mw/Mn, p/q, and Mn) Derivatives of such compounds can be synthesized according to the procedure described in xe2x80x9cSynthesis and characterization of low-viscosity fluoroether-based segmented oligomers,xe2x80x9d Die Angewandte Makromolekulate Chemie, 231 (1995) 47-60, (N.4000) S. Turri, M. Scicchizano, and C. Tonelli, incorporated by reference herein.
The reactive hydroxyl end-groups on these compounds can react with a BCBO compound, such as an acid-functional compound (II), according to Scheme 3:
The synthesis of the acid-functional BCBO compound (II) is described in Example 6 of U.S. Pat. No. 5,869,693.
The BCBO-end-capped PFPE macromers (III) and (IV) can be reacted with an acrylic copolymer, using UV irradiation, to form a graft polymer in which PFPE sidechains are grafted onto an acrylic polymer backbone. Standard coating techniques can be used to make a coating or film from a solution of the graft polymer. In some embodiments, compound (III) can be post-added into the irradiated solution. Further UV-curing can be performed just before the coated solution is subjected to heating. In this way, compound (III) is capable of introducing crosslinking into the coating system.
The following, non-limiting examples are provided to illustrate the invention and its preparation.